Basic calcium aluminum hydroxide dicarboxylates, a process for their production and their use

ABSTRACT

The invention describes basic calcium aluminum hydroxide dicarboxylates of the general formula 
     
         Ca.sub.x Al.sub.2 (OH).sub.2(x+3-y) A.sub.y ·m H.sub.2 O 
    
     wherein 
     x means 2 to 12, ##EQU1## m means 0 to 12, and A means an aliphatic, aromatic or heteroaromatic dicarboxylic acid anion or combinations thereof, 
     with the proviso that y≠ 1, if x= 2-8 
     and a process for their production. 
     The compounds according to the invention are particularly suited as stabilizers for halogen-containing thermoplastic resins, in particular PVC.

The invention relates to basic calcium aluminum hydroxidedicarboxylates, a process for their production and their use asstabilizers for halogen-containing thermoplastic resins, in particularpolyvinyl chloride.

Thermoplastic halogen-containing resins, in particular PVC, are instableto the influence of heat and light. A thermal decomposition occurs e.g.during processing of e.g. unstabilized PVC. This manifests itself in adiscolouring of the shaped article and in the deterioration of themechanical properties. In order to exclude this disadvantage, it isnecessary to incorporate heat stabilizers into the resin composition.For this purpose, organic and/or inorganic compounds of the metals lead,barium, cadmium, calcium, tin and zinc are customarily added alone or incombinations. Moreover, other co-stabilizers such as epoxides, organicsulphur compounds, polyols and phosphites are still added.

Basic lead compounds are preferably used to stabilize PVC articles, suchas pipes, plates, profiles and cable insulations. The most frequentlyused basic lead compounds are of the sulphate, phosphite or stearatetype.

DE-PS 12 19 223 and DE-OS 24 19 379 teach that PVC cable insulations areto be preferably stabilized with 2-basic lead phthalate, since thiscompound imparts excellent electrical properties to the cable.

It is mentioned in EP-A- 0 313 113 that 4-basic lead fumarate is themost effective basic lead compound for stabilizing plasticizedhalogen-containing vinyl polymer compositions. According to EP-A- 0 319086, 5-basic lead fumarate imparts a higher stability and a betterdegree of whiteness to shaped PVC articles than other known leadstabilizers.

The organic and/or inorganic compounds of the heavy metals lead, bariumand cadmium are classified as toxic. For this reason, it has beenattempted for a long time to replace them by non-toxic compounds. Thestabilizers on the basis of combinations of calcium and zinccarboxylates which are considered to be non-toxic are insufficient intheir effectiveness in most fields of application. Their disadvantagesmanifest themselves in an insufficient long-term stability and/or anunsatisfactory initial colour and colour retention. The combination ofthese metal soaps with effective co-stabilizers, which improve theinitial colour and long-term stability, is consequently imperative. Itis described in FR-A 2 403 362 to stabilize plasticized PVC for cableinsulations with a mixture of calcium zinc fatty acids, sorbitol and aβ-diketone. EP-A-0 256 872 describes the use of hydrotalcite and aβ-diketone for stabilizing PVC resins. The use of alkali alumo silicatesin connection with other co-stabilizers in PVC was also suggested (DE-A-31 13 442).

However, all non-toxic stabilization systems suggested so far havedisadvantages as compared with heavy-metal-containing stabilizers. Theymostly do not have the necessary long-term stability. A good initialcolour and a sufficient colour retention can only be achieved by usinglarge amounts of expensive "colour improver". The metal-containingco-stabilizers hydrotalcite and zeolite are disadvantageous in that theysplit off volatile components at the processing temperatures necessaryfor the processing of PVC, for instance, which leads to a bubbleformation in the shaped part. Moreover, shaped parts stabilized withe.g. polyol and/or zeolite absorb water, which leads to considerableproblems during the further processing.

DE-A- 40 02 988 (prior art within the purview of Section 3 II of theGerman Patent Act) describes basic calcium aluminum hydroxidedicarboxylates of the formula

    Ca.sub.x Al.sub.2 (OH).sub.2(x+2)A·m H.sub.2 O

wherein

x means 2 to 8,

m means 0 to 12, and

A means an aliphatic, aromatic or heteroaromatic dicarboxylic acid anionor combinations thereof,

a process for their production and their use as stabilizers forhalogen-containing thermoplastic resins.

The invention is based on the object of providing new compounds and aprocess for their production, which are particularly suited as astabilizer for halogen-containing polymers without having theaforementioned disadvantages of the known stabilizers, and are inparticular considered as non-toxic.

This object is attained on the one hand by providing basic calciumaluminum hydroxide dicarboxylates of the general formula

    Ca.sub.x Al.sub.2 (OH).sub.2(x+3-y) A.sub.y ·m H.sub.2 O

wherein

x means 2 to 12, ##EQU2## m means 0 to 12, and A means an aliphatic,aromatic or heteroaromatic dicarboxylic acid anion or combinationsthereof,

with the proviso that y≠1, if x=2-8.

In the aforementioned formula x means preferably 2 to 8, particularlypreferred 3 to 6 and m means preferably 2 to 4.

The dicarboxylic acid anions indicated with A are e.g. derived frommalonic acid, succinic acid, adipic acid, fumaric acid, maleic acid,phthalic acid, isophthalic acid, terephthalic acid and pyridinedicarboxylic acids. The fumarate and phthalate anion belong to thepreferred dicarboxylic acid anions.

Examinations by means of x-ray diffraction showed that thedicarboxylates according to the invention do not belong to thehydrotalcite type as regards their crystal structure.

It became surprisingly apparent that the calcium aluminum hydroxidedicarboxylates according to the invention impart heat stabilitiescomparable to those of basic lead compounds to halogen-containingthermoplastic resins and the shaped parts produced therefrom. Theinitial colours and the colour retention of e.g. rigid PVC shaped partsstabilized with one of the new compounds according to the invention areequivalent to the same shaped parts containing known, non-toxicstabilizer systems.

On the other hand, the object on which the invention is based isattained by a process for the production of the calcium aluminumhydroxide dicarboxylates according to the invention, which ischaracterized in that mixtures of calcium hydroxide and/or oxide,aluminum hydroxide and sodium hydroxide or of calcium hydroxide and/oroxide and sodium aluminate are reacted with the correspondingdicarboxylic acid in amounts corresponding to the production of thedesired compounds in an aqueous medium, and the reaction product isseparated and recovered in a known fashion. The reaction productdirectly obtained from the aforementioned reaction can be separated fromthe aqueous reaction medium according to known processes, preferably bymeans of filtration. The processing of the separated reaction product isalso carried out in a manner known per se, e.g. by means of washing ofthe filter cake with water and drying of the washed residue attemperatures of e.g. 60° to 130° C., preferably of 90° to 120° C.

Both a finely divided, active aluminum hydroxide in combination withsodium hydroxide and a sodium aluminate can be used for the reaction.Calcium can be used in the form of finely divided calcium oxide orhydroxide or mixtures thereof.

The reaction temperatures range preferably from about 25° to 100° C.,more preferred between about 40° and 85° C. Catalysts or acceleratorsare not required, but can possibly also be used. The water ofcrystallization can be removed wholly or partly from the compoundsaccording to the invention by means of thermal treatment.

When used as stabilizers, the dried calcium aluminum hydroxidedicarboxylates according to the invention do not split off any water atthe processing temperatures of 160° to 200° C. e.g. customary for rigidPVC so that no disturbing bubble formation occurs in the shaped parts.

The compounds according to the invention can be coated in known fashionwith surfactants to improve their dispersive power in halogen-containingthermoplastic resins.

According to the invention halogen-containing thermoplastic resins canbe stabilized with the calcium aluminum hydroxide carboxylates accordingto the invention. Polyvinyl chlorides, homo- and copolymers thereof andtheir mixtures with other polymers such as ABS (copolymer ofacrylonitrile/butadiene/styrene), CPVC (postchlorinated PVC), acrylatesand the like, which are produced in known fashion, are particularlysuited for this.

In addition to the compounds according to the invention, furtheradditives can of course be incorporated into the resin. Examples of suchadditives are organotin compounds, organic phosphites, epoxy compounds,amino compounds, polyhydric alcohols, metal soaps of C₈ -C₂₂ fatty acidswith the metals Ca, Zn, Mg or Al, antioxidants, UV absorbers, carbonylcompounds, antistatic agents, lubricants, plasticizers, pigments andfillers.

The invention is explained in greater details by means of the followingexamples.

A) Production of the Basic Calcium Aluminum Hydroxide DicarboxylatesAccording to the Invention Example 1

An aqueous suspension (5.0 l) of 222 g of calcium hydroxide (3 mole) and164 g of sodium aluminate (2 mole) is heated to 50° C. Subsequently 174g of fumaric acid (1.5 mole) are added in the form of a 10% aqueoussolution heated to 85° C. with stirring at a uniform feed speed in thecourse of 30 minutes. Thereupon the suspension is heated to 70° C. andstirred at this temperature for 2 hours. 10 minutes before the end ofthe reaction time, 4 g of sodium stearate are added for coating. Thesuspension obtained in this fashion is filtered off and washed with 1.8l of water. The filter cake formed in this fashion is dried in a dryingcupboard at 125° C. for 4 hours.

The analysis values of the product are indicated below.

    ______________________________________                                        Mole ratio                                                                             Found value                                                                            Calculated value                                            ______________________________________                                        Ca         3.0        3.0                                                     Al         1.9        2.0                                                     C          2.2        2.0                                                     ______________________________________                                    

Example 2

An aqueous suspension (7.2 l) of 444 g of calcium hydroxide (6 mole), 80g of sodium hydroxide (2 mole) and 156 g of active aluminum hydroxide (2mole) is heated to 70° C. Subsequently, 498 g of phthalic acid (3 mole)in the form of a 8% aqueous solution (temperature 85° C.) are added withstirring at a uniform feed speed in the course of 30 minutes. Thereuponthe suspension is heated to 80° C. and stirred at this temperature for 2hours. 10 minutes before the end of the reaction time, 4 g of sodiumstearate are added for coating. The suspension obtained in this fashionis filtered off, washed with 2.3 l of water, and the filter cake isdried in a drying cupboard at 130° C. for 4 hours. The analysis valuesof the product produced in this fashion are indicated below.

    ______________________________________                                        Mole ratio                                                                             Found value                                                                            Calculated value                                            ______________________________________                                        Ca         6.0        6.0                                                     Al         2.1        2.0                                                     C          16.4       16.0                                                    ______________________________________                                    

B) Use of the Compounds According to the Invention as Stabilizers

The heat stability and the initial colour of shaped PVC bodies to whichthe compounds of the invention had been added are evaluated in thefollowing examples.

For the evaluation of the heat stability the mixtures used in thefollowing examples are homogenized and plastified in a laboratoryrolling mill at 180° for 5 minutes. Square sample sheets with an edgelength of 15 mm are cut from the about 1 mm thick milled sheet producedin this fashion. These sample sheets are tempered in a drying oven at190° C. At 10-minute intervals one sheet each is removed and affixed toa test card one after the other. This procedure is repeated until thesample sheets turned black.

Example 3

    ______________________________________                                                       Parts by weight                                                               A       B      C                                               ______________________________________                                        PVC (K 68)       100       100    100                                         Chalk             6         6      6                                          TiO.sub.2         3         3      3                                          Stearyl stearate 0.5       0.5    0.5                                         Bisphenol A      0.1       0.1    0.1                                         Lead stearate    1.0       --     --                                          Dibasic lead phthalate                                                                         2.0       --     --                                          Calcium stearate 0.5       0.8    0.8                                         Zinc laurate     --        0.8    0.8                                         Ca.sub.3 Al.sub.2 (OH).sub.11 (C.sub.4 H.sub.2 O.sub.4).sub.0.5                                --        3.0    --                                          Ca.sub.6 Al.sub.2 (OH).sub.14 (C.sub.8 H.sub.4 O.sub.4).sub.2.0                                --        --     3.0                                         Calcium acetyl acetonate                                                                       --        0.1    0.1                                         ______________________________________                                    

The aforementioned compositions of A to C were tested according to theindicated method. The results are summarized in table I.

                  TABLE I                                                         ______________________________________                                        Results of the evaluation of the thermal stability                            Composi-                                                                             Time (min.)                                                            tion   0     10    20  30  40  60  80  100  120  140  160                     ______________________________________                                        A      1     1     1   1   3   3   3   3    3    5    5                       B      1     1     1   1   2   2   2   4    4    4    6                       C      1     1     1   2   2   2   2   4    4    4    6                       ______________________________________                                         1 = white                                                                     2 = slightly yellow                                                           3 = slightly grey                                                             4 = yellow                                                                    5 = grey                                                                      6 = brown                                                                

Example 4

    ______________________________________                                                       Parts by weight                                                               D       E      F                                               ______________________________________                                        PVC K 70         100       100    100                                         Chalk            40        40     40                                          TiO.sub.2         2         2      2                                          Diisodecyl phthalate                                                                           50        50     50                                          Bisphenol A      0.3       0.3    0.3                                         Pentaerithritol  0.1       0.1    0.1                                         2-basic lead phthalate                                                                         2.0       --     --                                          Lead stearate    1.0       --     --                                          Calcium stearate 0.5       0.8    0.8                                         Zinc laurate     --        0.8    0.8                                         Ca.sub.3 Al.sub.2 (OH).sub.11 (C.sub.4 H.sub.2 O.sub.4).sub.0.5                                --        3.0    --                                          Ca.sub.6 Al.sub.2 (OH).sub.14 (C.sub.8 H.sub.4 O.sub.4).sub.2.0                                --        --     3.0                                         ______________________________________                                    

The aforementioned compositions of D to F were tested according to theindicated method, and the thermal stability was assessed. The resultsare summarized in table II.

                  TABLE II                                                        ______________________________________                                        Composi-                                                                             Time (min.)                                                            tion   0      10    20   40  60  80  120  160  180  200                       ______________________________________                                        D      1      1     1    1   1   3   3    3    3    5                         E      1      1     1    1   1   2   2    4    4    6                         F      1      1     1    1   2   2   2    4    4    6                         ______________________________________                                         1 = white                                                                     2 = slightly yellow                                                           3 = slightly grey                                                             4 = yellow                                                                    5 = grey                                                                      6 = brown                                                                

We claim:
 1. A basic calcium aluminum hydroxide dicarboxylate compoundrepresented by the general formula

    Ca.sub.x Al.sub.2 (OH).sub.2(x+3-y) Ay ·m H.sub.2 O

wherein X is 2 to 12; ##EQU3## with the proviso that y≠1 if x=2 to 8; mis 0 to 12; and A is an aliphatic, aromatic or heteroaromaticdicarboxylic acid anion or combination thereof.
 2. The compoundaccording to claim 1, wherein x is 2 to
 8. 3. The compound according toclaim 1, wherein x is 3 to
 6. 4. The compound according to claim 1,wherein m is 2 to
 4. 5. The compound according to claim 1, wherein A isa fumarate anion.
 6. The compound according to claim 1 wherein A is aphthalate anion.
 7. A process for the production of the compoundaccording to claim 1 characterized in that mixtures of calcium hydroxideand/or oxide, aluminum hydroxide and sodium hydroxide or of calciumhydroxide and/or oxide and sodium aluminate is reacted with thecorresponding dicarboxylic acid in amounts corresponding to theproduction of the desired compounds in an aqueous medium, and thereaction product is separated and recovered in a manner known per se. 8.A process according to claim 7, characterized in that the reaction iscarried out at a temperature between about 25° and 100° C.
 9. A processfor stabilizing resins comprising adding a stabilizing effective amountof the compound of claim 1 to a halogen-containing thermoplastic resin.10. The process according to claim 9 wherein the halogen-containingthermoplastic resin is polyvinyl chloride.